The present invention relates to a total hip prostheses adapted to be implanted endo-articularly and its auxiliary device. Upon deterioration of the articulation of the hip, for example in the case of arthrosis or rheumatoid arthritis, it may be necessary to replace the coxo-femoral articulation by a prosthesis.
Certain prostheses now known comprise:
a cotyloid implant constituted by a metallic cup provided with primary anchoring means in the acetabulum and having externally an overall hemispheric surface and internally a concave recess,
an insert forming an intermediate implant generally of plastic, such as polyethylene, provided with means for connection with the cup and having externally a surface complementary to that of the recess of the cup in which it is received and internally a substantially hemispherical recess, and
a metallic femoral implant constituted by a femoral rod implanted in the medullar channel of the femur and a prosthetic neck surmounted by a spherical femoral head which will be articulated in the recess of the insert.
Implanting such a prosthesis requires an expensive total arthroplasty technique of the hip, which is subject to a number of requirements.
Thus, it is necessary to provide an ablation of the femoral head and a portion of the femoral neck to implant the femoral rod in the midportion of the femur, even if the degeneration of the articulation hasn""t reached the neck or head of the femur.
In addition to ablation of the head of the femur, it is necessary to do the same for all of the articular capsule.
On the other hand, in this open surgery, it is necessary to provide access of about ten centimeters and to dislocate the articulation to be able to introduce the various instruments for cutting and the various implants.
The present invention therefore has for its object to provide a new total hip prosthesis permitting limiting the resection to only the injured articular surfaces so as to preserve the integrity of the head of the femur and of the capsule, and to carry out minimal arthrotomy.
To this end, the invention has for its object a total hip prosthesis comprising: a cotyloid implant constituted a metallic cup provided with primary anchoring means in the acetabulum and having externally an overall convex surface and internally a generally concave recess,
an insert forming an intermediate implant for example of a plastic such as polyethylene, provided with connection means with the cup and having externally a shape complementary to the recess of the cup in which it is received and internally a concave bearing recess, and
a metallic femoral implant adapted to be received slidably in the bearing recess of the insert and implanted in the femoral bone,
characterized in that the femoral implant is constituted by a cap having externally a convex surface adapted to come into sliding bearing engagement in the recess of the insert and internally a concave surface adapted to implant itself in the spongy bone of the femoral head.
According to another characteristic of the invention, the femoral implant comprises a small screw-threaded rod which projects perpendicularly to the center of its concave surface and a separate element forming a screw-threaded nut internally for screwing on said screw-threaded rod and externally screw-threaded to screw into the femoral head along the axis of the femoral neck.
Preferably, the pitch of the external screw-threading of the nut is greater than that of its internal screw-threading.
According to another characteristic of the invention, the cotyloid implant is pierced at its center for the passage of a screw-threaded lug for primary anchoring in the acetabulum.
On the convex surface of the cotyloid implant and the concave surface of the femoral implant can be provided asperities or small points to improve the anchoring respectively in the acetabulum and the femoral head.
According to still another characteristic, the mentioned connection means are snap-in means of the mortise and tenon type at the periphery of the base of the cup and of the insert.
According to another characteristic, each implant comprises at its periphery a local coupling means such as substantially radial female thread, to permit its coupling to a carrying arm.
The present invention also relates to an auxiliary device for endo-articular implantation of the prosthesis mentioned above, characterized in that it comprises:
a plurality of instruments adapted to be introduced along the axis of the femoral neck from the region of the trochanter base toward the coxo-femoral articular space such that their free distal end serves to center and guide the prosthesis during its implantation,
a carrying arm that can support removably at its distal end the mentioned implants or a drill for introducing them by a lateral access route in the mentioned articular space, and
a support structure adapted to be positioned parallel to the axis of the femur and at the lower end of which is selectively ensleeved or introduced freely in rotation and/or slidably one of the mentioned instruments and at the upper end of which is ensleeved the carrying arm slidably and inclinably to engage the implant or the drill on the distal end of an instrument opening into the articular space.
The distal end of the instruments defines a point of intersection with the drills or the implants and gives the central working point in the coxo-femoral articulation.
In a particular embodiment, the distal end of the carrying arm is screw-threaded to screw into a female thread provided at the periphery of the implant or of the drill to be supported.
According to another characteristic, the device can comprise a hemispheric femoral drill whose internal surface is adapted to grind down the head of the femur, said drill being pierced at its center to receive secured in rotation therewith the distal end of an instrument which is adapted to be connected at its proximal end to a rotatable drive motor.
In this case, the device can comprise moreover a bearing arm ensleeved parallel to the carrying arm at the upper end of the support structure and constituted by a rod whose distal portion is in the form of an arc of a circle matching the shape of a meridian from the external surface of the femoral drill and of which the distal end is adapted to bear in a pivotal manner on the center of said drill.
The support structure can thus also comprise a means forming a vise whose movable jaw is constituted by the bearing arm and the fixed jaw is secured to said structure, the two jaws being adapted to be selectively brought together so as to press the femoral drill against the head of the femur.
According to another characteristic of the invention, the device can comprise a hemispheric cotyloid drill whose external surface is adapted to grind down the cotyloid cavity, said cotyloid drill being pierced at its center to receive and be secured to in rotation the distal end of an instrument which is adapted to be connected at its proximal end to a rotatable drive motor.
In this case, the device can moreover comprise an instrument forming a bit adapted to traverse the central hole of the cotyloid drill to hollow in the acetabulum bone a central cotyloid hole for reception of a screw-thread lug of the cotyloid implant.
According to still another characteristic, the distal end of the instrument has a shape complemental to the head of the screw-threaded lug mentioned above, for screwing into the centro-cotyloid hole.
In a particular embodiment, the device comprises a cotyloid impactal element temporarily secured in the recess of the insert by frangible peripheral points. The impact element can be provided with a recess of a shape complementary to the distal end of the instrument or a small screw-threaded rod which projects perpendicularly to the center of its lower surface.
The device thus comprises preferably an instrument whose distal end is internally screw-threaded in a manner complementary to the screw-threaded rod of the femoral implant and/or the impactor element.
According to still another characteristic, the device of the invention comprises an instrument whose distal end supports removably and is secured in rotation to the nut no of the femoral implant to screw this latter into the head of the femur and on the screw-threaded rod of the femoral implant.
It can be provided that in the engaged position of the drill or the implant on an instrument, this latter and the carrying arm define between them an angle of about 60xc2x0.
To this end, the support structure can have an elbowed shape whose upper and lower branches define an angle of about 120xc2x0.